Switching mode power supplies can generate high frequency noise which travels over the power lines and interferes with the operation of computers and other electronic devices connected to the power lines. EMI in the environment induces or couples electrical noise into the power lines. EMI generated by the noise signals is generally an unwanted disturbance that may affect an electrical circuit. The disturbance can interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit.
Electrical noise is classified into two types according to the conduction mode. Electrical noise which comes in one power line wire and returns to the noise source through the other power line wire is termed as differential noise. Differential noise travels in opposite directions in its forward and return paths. Electrical noise which comes through one power line and returns to the noise source through a reference ground path is termed as common mode noise. The common mode noise travels in the same direction in the power line wires.
In an electrical power system, a load with a low power factor draws more current than a load with a high power factor for the same amount of useful power transferred. Accordingly, PFC circuits are often used to reduce the power factor of an electrical power system.
A conventional boost power factor correction (PFC) system 100 that uses a diode bridge rectifier is illustrated in FIG. 1. FIG. 2 illustrates a bridgeless boost PFC system 200.
Various techniques have been used to improve the efficiency and/or filter common mode conducted EMI in a PFC circuit.